This invention relates to a new and improved blood oxygenator having an improved, reuseable heat exchanger and a dual sparger system for increasing oxygenation efficiency and CO.sub.2 removal.
Blood oxygenators are usually designed with the intent of using components that are premanently secured in the device, the principal one being the heat exchanger. This item constitutes one of the major expenses in a blood oxygenator; however, after use, the heat exchanger is usually discarded along with the body of the oxygenator. If the heat exchanger could be readily detached from the blood oxygenator and reused, the cost of the equipment would be reduced considerably. Also, since fewer heat exchangers would be required overall in a particular facility, they could be manufactured to a much higher quality than if they were mass produced. This in turn would reduce the possibility of producing a defective component, and also would reduce quality control costs. A replaceable heat exchanger should be capable of quick and easy removal from the oxygenator and connecting water lines. Also, the movement of cooling water through the heat exchanger should be simple and efficient, and preferably with little opportunity for scale build up.
In the case of a finned heat exchanger, the transfer efficiencies of oxygen will depend on the amount of finned surface available for contact between the blood and the oxygen bubbles. Hence, a heat exchanger configuration having spirally wound fins should increase the residence time for the blood and improve oxygen transfer efficiencies compared to a finned heat exchanger having parallel fins. Similarly, a spirally wound finned heat exchanger is preferred for efficiency of heat exchange.
In U.S. Pat. No. 4,254,081, the inventor herein described an elliptically shaped heat exchanger for a blood oxygenator having spirally wound fins. However, it is not practical to manufacture such a device (as opposed to a heat exchanger having parallel fins) because of severe fin distortion along the major axis of the ellipse.
Blood oxygenators require an efficient oxygen uptake into the blood, and an equally efficient CO.sub.2 removal. However, the most effective mean sparger pore size for oxygen uptake is about 1.mu., and the most effective mean sparger pore size for CO.sub.2 removal is about 40.mu., with a wide mean variation. Heretofore, this disparity in pore sizes made it difficult to simultaneously achieve both effects in a single sparger because a gas will move along the lines of least resistance, namely along the paths adjacent the largest pores.